1. Field of the Invention
The present invention relates to a brake system for a vehicle equipped with a continuously variable belt transmission (hereinafter referred to as “CVT”).
2. Related Art
As disclosed by JP S48-44548 Y, a conventional CVT to be equipped on a vehicle such as a golf car or golf cart includes a driver pulley, a driven pulley and a belt interposed between the drive and driven pulleys. A pulley shaft of the driver pulley serves as an input shaft of the CVT, i.e., a CVT input shaft, to be drivingly connected to a prime mover such as an internal combustion engine arranged upstream of the CVT in a power train of the vehicle. A pulley shaft of the driven pulley serves as an output shaft of the CVT, i.e., a CVT output shaft, to be drivingly connected to an axle and drive wheels arranged downstream of the CVT in the power train of the vehicle.
At least one of the driver and driven pulleys has a variable pitch diameter so that a speed ratio of the CVT between the CVT input and output shafts can be changed by changing the pitch diameter. The driver pulley includes a pair of half pulleys. One half pulley is axially movable along the pulley shaft (i.e., CVT input shaft), and the other half pulley is axially immovable along the pulley shaft. As the output rotary speed of the prime mover is reduced, the centrifugal force applied to the axial-movable half pulley is reduced so that the axial-movable half pulley moves away from the axial-immovable half pulley. Therefore, the driver pulley functions as a clutch-disengagement action to isolate the belt, the driven pulley and the CVT output shaft from the rotation of the CVT input shaft driven by the prime mover. If the prime mover is an engine, such a clutch-disengagement action of the driver pulley advantageously ensures a stable idling of the engine free from load that the vehicle receives at the drive wheels.
However, when the vehicle descends a slope at an engine idling speed, an operator of the vehicle has to repeat depressing a brake pedal for braking the axle because the belt, the driven pulley and the CVT output shaft receive no power from the idling engine while the driver pulley functions as the clutch-disengagement action. Such a repeat of braking may possibly cause a brake fade or a vapor lock. Unless an operator carefully manipulates the brake pedal, the descending vehicle may happen to be accelerated to an expected high speed. In other words, the vehicle equipped with the CVT does not have means having an effect similar to an engine brake of a vehicle equipped with a gear transmission.